A simulation analysis of sequencing rules for ASRS in a pull-based assembly facility

Just-in-time (JIT) systems operate on a pull-based production control. The material needed is expected to be at its production site when and only when it is needed. When an automated storage retrieval system (ASRS) is used as a valve warehouse to support JIT manufacturing, the delivery time becomes critical. This paper presents an investigation on the effect of job sequencing rule on delivery performance of an ASRS, which is used as a valve warehouse to support a pull-based Kanban-driven assembly line. The analysis was based on computer simulation. The interaction of the sequencing rules with other control variables was also examined     

Fixture modelling for an automotive assembly line

This paper proposes an efficient fixture modelling procedure for automotive body assembly lines. A fixture model consists of two sub-models; a geometric model and a kinetic model that should be remodelled frequently whenever design changes occur. We develop an algorithm extracting the kinetic model from the geometric model of a fixture to reduce the fixture modelling time and effort. Although the geometric models of fixtures used in automotive assembly lines vary, most follow the same kinetic mechanism, the so-called slider-crank mechanism; this is a four-axis system of three revolute and one prismatic joint. The prismatic axis of a fixture represents a pneumatic actuator involving a piston and a cylinder. It is very important to identify the prismatic axis from a given geometric model to extract the kinetic model of a fixture. We use the concept of the ‘moment of inertia’, which is a measure of an object's resistance to changes in its rotation rate, to identify the prismatic axis. Since the exact computation of the moment of inertia for an arbitrary solid model requires complicated computations, we introduce an approximating method for the moment of inertia. The proposed procedure has been implemented and tested with various examples.     

Evaluating assembly sequences for automatic assembly systems

Selecting the assembly sequence and associated automatic assembly stations necessary to assemble a candidate product design is a critical step in the life cycle of a product. We present a method that determines the best sequence and set of stations using cost and performance measures. The method uses a multi-echelon optimization procedure based on simulated annealing. We show how simulated annealing can be used for such problems and present examples in which we determine the optimal assembly sequence for a product in an automated manufacturing environment.     

Combining items for lot sizing in multi-level assembly systems

Multi-level lot sizing problems are difficult to solve optimally when the product structure contains more than a few items. This paper identifies conditions on the cost parameters which, when applicable, allow items to be combined for purpose of optimization, thereby reducing the size of the problem.     

Control logic verification for an automotive body assembly line using simulation

In this paper, an approach is proposed that verifies the controller logic processes for the automobile industry via simulation. For this purpose, a state-based object model that creates a virtual car body assembly line is proposed and a verification methodology using observed signal sequences during the simulation is proposed. This approach was applied to an assembly line controlled by a PLC and the effectiveness of the proposed system was explained in a case study.     

Discrete electromagnetism-like mechanism algorithm for assembly sequences planning

Assembly sequence planning (ASP) plays an important role in digital manufacturing. It is a combinatorial optimisation problem with strong constraints aiming to work out a specific sequence to assemble together all components of a product. The connector-based ASP, which uses the connector to simplify the complex assembly problem, is one of the most important and hardest types. In order to solve this problem effectively, a discrete electromagnetism-like mechanism (DEM) algorithm is proposed. A charge formula and a force formula are redefined in DEM algorithm. An adjacency list is applied to handle the precedence relationship and prevent infeasible solutions. Two movements based on path relinking are employed. Moreover, with two different guided mutations, the population diversity can be guaranteed. Five examples are used to test and evaluate the performance of DEM. The comparisons among the proposed DEM, traditional genetic algorithms (GAs), guided GAs, memetic algorithms and artificial immune systems show that DEM outperforms among these algorithms in terms of running time, computation accuracy, convergence speed and parameter robustness.     

Optimisation of assembly sequences for compliant body assemblies

Multi-sequence modelling is proposed to optimise assembly sequences for compliant body assemblies such as automotive and aircraft bodies. Multi-sequence modelling is composed of assembly modelling, assembly sequences, tolerance analysis, and assembly operations. Assembly modelling describes the geometric modelling through the liaison graph, which is based on assembly sequence optimisation. Assembly sequences provide information for assembly sequence optimisation. Three-dimensional tolerance analysis is employed to evaluate assembly operations, which is different from previous conceptual tolerance analysis. A genetic algorithm is presented to optimise assembly operations among components. Results show that different sequences lead to a different tolerance of key product characteristics because assembly operations among components are not identical. This paper provides the flowchart of optimising assembly sequences according to the tolerance of key product characteristics.     

Using distributed search methods for balancing mixed-model assembly lines in the automotive industry

Currently, modern companywide PC networks usually possess significant unused calculation capacity. Since the connected personal computers are mainly used for office applications, considerable off-peak times occur. Consequently, in order to solve planning problems more efficiently, it is promising to apply distributed search procedures that make use of those available off-peak times. This applies in particular to complex problems where insights into the structure of the solution space are lacking. The paper at hand illustrates the application of distributed search methods to automotive assembly line balancing. Modern mass customization programs in the automotive industry frequently comprise more than a billion theoretical variants. Since this causes an oscillating capacity demand at the line, deliberately designing the layout of a mixed-model assembly line is of significant importance. The paper at hand provides a new mixed-model assembly line balancing approach that integrates specific aspects relevant for the automotive industry. However, by integrating several -hard subproblems like a detailed personnel planning or a flexible process planning of each task, the resulting model has significant complexity. Consequently, in order to find appropriate line layouts in reasonable time, specifically designed distributed solution approaches are provided and evaluated. Among these approaches, particularly the use of a specific clustered Tabu Search algorithm attains promising results. By making use of an adaptive dynamic load balancer, substantial improvements of the solution quality can be obtained even under unfavorable circumstances like oscillating background loads in the PC network.     

Labour productivity in modular assembly: a study of automotive module suppliers

Modular assembly is being applied to an increasing number of vehicles and part manufacturers to manage the ever-changing demands of the automotive industry. In spite of many researches performed on the supply chain management and logistics aspects of modular production, there is no research discussing modular production line concepts used by module suppliers. In this paper, labour productivity of two assembly line concepts including the conveyor line and box assembly line is studied under modular production environment. Both line concepts and respective assembly processes are described in detail. Mathematical models showing the total work faced by these two assembly line concepts are developed and compared. Two productivity scales are defined: the maximum achievable productivity and the actual productivity. The labour productivity rates of these assembly line concepts on above productivity scales obtained from calculations and a simulation are compared as a performance measure.     

Managing design of assembly sequences for product lines that delay product differentiation

The integration of product design and operations could potentially enhance the ability of manufacturers to provide large variety in the product line while keeping their operations competitive. At the plant level, an improved assembly sequence can lead to superior operational response to customer demands. While this has been intuitively accepted, there is a scarcity of models that can adequately reflect the operational benefits of a costlier yet better design. In this paper, we present integrated models applicable at a plant level that can provide quantification of certain operational benefits. Further, through a computational study, we also provide qualitative insights on several issues such as the effect of: (i) features in the product line; (ii) variance of demand for the different features on the optimal assembly design; (Hi) set-up times; and (iv) life cycle of the product line.     

Factors impacting manual picking on assembly lines: an experiment in the automotive industry

Manual picking on assembly lines is an important part of the assembly operator's work. In the automotive industry, alternative material exposure strategies are continually evaluated in order to facilitate the assembler's work and minimise non-value-adding time, resulting in increased use of smaller bins or containers at workstations, instead of large pallets. The assembly operator's retrieval of components from bins, containers or pallets is known as manual picking. Previous work in this area has focused on picking from pallets placed on the floor; therefore, there is a need to include other forms of material exposure. The purpose of this paper is to explain what material exposure factors have an impact on manual picking times on assembly lines. A full factorial experiment, testing seven factors in 128 experiments, was conducted in an automotive assembly line setting. The factors with the greatest impact on manual picking time were packaging type; angle of exposure; height of exposure; and part size. This study contributes by addressing the importance of six factors influencing manual picking times, enhancing knowledge derived from MTM and elsewhere. The results from this study can be useful for designing manual picking operations, not just at assembly lines but also other situations where discrete manual picking occurs such as at workstations or bench assembly. Managerial contributions are evident in the examination of factors important in designing new production systems, including materials supply processes and assembly processes. A further managerial application is the use of the results in managing assembly lines.     

Commercial spectrophotometer for particle sizing

Particle-size distribution and the concentration of polystyrene particles suspended in water were accurately recovered from the inversion of spectral extinction data measured with a commercial spectrophotometer. The instrument was modified by placing a spatial filter in the collection optics to prevent low-angle scattered light from affecting the measurement of transmitted power. The data were inverted by use of a nonlinear iterative algorithm. When the extinction coefficient is measured in the lambda range of 0.3-1.1 mum, the particle distributions can be retrieved over a diameter range of 0.6-2.8 mum for a wide interval of sample concentrations. The average diameters are recovered with a precision of better than +/-1% and with accuracies consistent with the uncertainties by which the nominal diameters are known. The relative standard deviations of distributions corresponding to monodisperse samples are +/-5-10%, whereas the accuracy on the measured concentrations is ~5%.     

Balancing of mixed-model parallel U-shaped assembly lines considering model sequences

As a consequence of increasing interests in customised products, mixed-model lines have become the most significant components of today’s manufacturing systems to meet surging consumer demand. Also, U-shaped assembly lines have been shown as the intelligent way of producing homogeneous products in large quantities by reducing the workforce need thanks to the crossover workstations. As an innovative idea, we address the mixed-model parallel U-shaped assembly line design which combines the flexibility of mixed-model lines with the efficiency of U-shaped lines and parallel lines. The multi-line stations utilised in between two adjacent lines provide extra efficiency with the opportunity of assigning tasks into workstations in different combinations. The new line configuration is defined and characterised in details and its advantages are explained. A heuristic solution approach is proposed for solving the problem. The proposed approach considers the model sequences on the lines and seeks efficient balancing solutions for their different combinations. An explanatory example is also provided to show the sophisticated structure of the studied problem and explain the running mechanism of the proposed approach. The results of the experimental tests and their statistical analysis indicated that the proposed line design requires fewer number of workstations in comparison with independently balanced mixed-model U-lines.     

Optimising part feeding in the automotive assembly industry: deciding between kitting and line stocking

In a synchronous and fast-paced assembly line operation, it is crucial that the right parts are being supplied at the right time and at the right place. In automotive assembly, the need for efficient material handling part delivery is particularly great because of extensive product customisation and the lack of space to stock all the required parts at the assembly line. This paper introduces a mathematical cost model for evaluating the assignment of parts to one of two possible material supply systems: kitting or line stocking. Case data from an automotive company in Belgium is used to test the model. The results demonstrate that hybrid policies, where some parts will be kitted while others will be stocked in bulk at the line, are preferred to the exclusive use of either material delivery system. The factors influencing the preferred delivery method for individual parts are explored. Numerical results are presented.     

Efficient heuristics for dynamic lot sizing

Dynamic lot sizing heuristics commonly implemented in standard MRP software perform well under conditions of systematic demand only. A survey and numerical test of methods proposed in the literature shows that techniques are available which cope efficiently with both systematic and erratic demand. The paper discusses theoretical and practical ramifications of the dynamic lot sizing problem, surveys heuristics published in the U.S. and West German literature, reports summarily on the findings of extensive simulation experiments involving these heuristics, and, as a conclusion from analytical and numerical results, proposes an algorithm which enhances performance under conditions of erratic demand.     

Composites for automotive on-engine applications

Over the past fifteen years extensive developments have demonstrated the suitability of moulded reinforced polymer composites as replacements for cast and fabricated “bolt-on” engine components in mass produced vehicles and yet little has reached production. The article discusses some of the complex and interacting relationships between material selection, processing options, component design, investment and component costs which influence progress down the route to materials substitution. In a review of the progress already made, the problems resolved and those remaining, it is suggested that the next few years should see this work reach commercial fruition.